Irradiation method and apparatus



July 28, 1959 D. R. DEWEY ll, ET AL 2,897,365

IRRADIATION METHOD AND APPARATUS Filed Oct. 8, 1956 I I I i l l v l i ll 1 I 1 A l I l l I IRRADIATION METHOD AND APPARATUS DavisR. Dewey EH,Lincoln, and John G. Trump, Winchester, Mass, assignors to High VoltageEngineering Corporation, Cambridge, Mass, a corporation of MassachusettsApplication October-8, 1956, Serial No. 614,661

3 Claims. (Ci. 25049.5)

This invention relates to irradiation with high-energy electrons and inparticular to irradiation with highenergy electrons from a singleelectron accelerator in such a manner-as to utilize the ionizing energyof the high-energy electrons in a more efiicient manner. Morespecifically stated, the invention comprehends directing a beam ofhigh-energy electrons whose cross-section is extended in at least oneplane, from a single electron source towards an object to be irradiatedand subjecting said beam to the action of a combination of magneticfields so arranged that the electrons bombard the object to'beirradiated from substantially all aspects in said plane. The object tobe irradiated may be stationary, or it or a series of objects may bemoved continuously or discontinuously in a direction transverse to saidplane. The invention is particularly Well suited to the irradiation ofcontinuous lengths of a product or products having ,a generally circularcross-section, such as plastic tubing, cable, or insulated wire, or suchas an axially aligned succession of bottles, ampoules, vials,collapsible containers, or similar objects. The term generally circularcross-section as used herein means a circular, elliptical, ovoida-l,polygonal or similar cross-section. Accordingly, in the followingdetailed description the invention will be described with particularreference to the irradiation of a continuous length of hollow plastictubing, but the invention is not limited to the irradiation of any.particular type, shape, or composition of object to be irradiated.

The invention will also be described with particular referenceto anelectron accelerator in which the beam of electrons whose cross-sectionis extended in at least one plane, is produced by imparting a scanningmovement to an electron beam; but the invention is not limited to anyparticular means for producing the electron beam of extendedcross-section, and includes other means for accomplishing this result,such as focusing an electron beam by an electron-optical system inaccordance with the teachings of U.S. Patent No. 2,737,593 to Robrnson.

The invention may bestbe understood from the following detaileddescription thereof, having reference to the accompanying drawing, inwhich Fig. 1 is a somewhat diagrammatic side view of apparatus embodyingthe invention and including an electron accelerator adapted -to.producea beam ofelectrons of extended cross-section and means for producing acombination of magnetic fields for directing the electrons onto theobject to be irradiated from substantially all aspects in the plane ofthe sheet;

Fig. 2 is a plan view of the means for producing a suitable combinationof magnetic fields shown in Fig. 1; and

Fig. 3 is a diagram showing the electron trajectories in the apparatusof Fig. 1.

It is now becoming established that all types of living organisms areaffected by gamma rays and high energy electrons and that lethal effectscan be produced on unatent wanted organisms by doses which will raisethe tem-v perature of water only a few degrees centigrade. The growingavailability of streams of high energy electrons makes possible thepractical application of this knowledge to the sterilization of manyimportant products, such as pharmaceuticals, surgical instruments,animal tissues for transplant purposes, as well as for the preservationof certain foods. Only high energy electron sources, as distinct fromgamma ray sources, appear to possess enough total power output to handleeconomically the considerable amounts of material which may requiresterilization or preservation.

Moreover, the possibility of using various forms of ionizing radiationto promote chemical reactions has recently been explored, includinghighly endothermic chem ical reactions which require large quantities ofenergy in concentrated form and exothermic chemical reactions which'are'triggered by the initial application of concentrated energy. Amongavailable sources of ionizing radiation, high energy electrons seem tobe the best medium for delivering ionizing energy in an efficient andcontrolled manner to a substance or substances for the purpose ofpromoting chemical reactions.

Measurements of the properties of high energy electrons have disclosedthat their range in typical materials is small compared to that of gammarays. A Z-millionvolt electron has a maximum range in water of 1 cm.Beyond this limiting distance there is no ionizing elfect, while themaximum ionizing effect occurs at one-third this angle. maybeconstructed for many millions of volts, such higher energy apparatusbecomes progressively more expensive .and also often has a lower outputelectron current capacity.

. A common method of, in eifect, doubling the range of penetration of anavailable stream of electrons is to irradiate the object from both sidesas by reversing the object and irradiating again, or by irradiating theobject simultaneously from two electron sources. However, the former islimited to the irradiation of material in-rigid form, and the latterentails the additional expense and space requirements of a secondelectron source. Furthermore, an interruptionor modulation of electronintensity would: not afiect both aspects simultaneously, unless theproduct is irradiated simultaneously, from two electron sources withspecial electronic coupling being introduced between the two sources;consequently, it would be difiicult to re-irradiate the partiallyirradiated material to bring its dose up to "the proper level.

The difficulties caused by the fixed range in matter of an electron beamof fixed energy is augmented in the radiated inorder to cross-link themolecules of which the plastic is composed in order to-improve theprop-- erties of the plastic. For example, the electron energy requiredto penetrate a solid cable with a beam of-.elec--- trons directedonto-the cable from one aspect is determined, by the diameter. of thecable, but most of, the.

electron-beam-need penetrate only a fraction of this depth. Similarly,the electron energy required to penetrate a hollow cable with a beam ofelectrons directed onto the cable from one aspect is considerablygreater than that required to penetrate the thickness of the Wall of thecable.

Referring more particularly to the drawings, one embodiment of apparatusfor practising the method of the invention is shown in Figs. 1 and 2,wherein an electrostatic accelerator for the acceleration of electronsto high energy is indicated at 1. The electron accelerator 1 maycomprise an electrostatic generator of the type disclosed in US. PatentNo. 2,252,668 to Trump in con- Although practical high-energy electronsources.

junction with an acceleration tube of the type disclosed in US. PatentNo. 2,517,260 to Van de Graatf and Buechner. Alternatively, the electronaccelerator 1 may comprise a microwave linear accelerator of the typedescribed by Walkinshaw at volume 61, pages 246254, by R. Shersby-Harvieat volume 61, pages 255-270, and by Mullett and Loach at volume 61,pages 271-283 of The Proceedings of The Physical Society (1948), or anyother suitable electron accelerator, such as a resonant transformer.

Electrons are accelerated by the electron accelerator 1 in a manner notnecessary to explain herein in detail and enter an evacuated tubeextension 2 as a beam of high-energy electrons. Said tube extension 2terminates in a flared portion 3 the extremity of which is closed offfrom the atmosphere by an electron window 4. A beam-scanning device 5imparts a scanning movement to the electron beam in the plane of thedrawing in Fig. 1 in accordance with the teachings of US. Patents Nos.2,602,751 and 2,729,748 to Robinson.

A product, material or substance which is to be irradiated, shown inFigs. 1 and 2 as a hollow plastic cable 6, is positioned in the path ofthe electron beam 7, which issues from the electron window 4 as a beamwhose cross-section is extended in the plane of the drawing in Fig. 1,by suitable supports 8. Any conventional means (not shown) may beemployed to impart longitudinal traveling movement to the cable 6. Thewidth of the cable 6 is less than the width of the electron sheet 7, asshown in Fig. 1, so that some of the electrons impinge directly onto thetop of the cable 6, While some of them travel to the left and some tothe night of the cable 6.

Two magnets 9, 10 are supported so as to produce a combination ofmagnetic fields in the path of the electron beam 7. The magnets 9, 10are so designed as to produce a magnetic field between the left-handpole faces 11, 12 which is directed out of the plane of the drawing inFig. 1 and downward in Fig. 2, and also to produce a magnetic fieldbetween the right-hand pole faces 13, 14 which is directed into theplane of the drawing in Fig. 1 and upward in Fig. 2. Therefore,electrons which travel to the left of the cable 6 are deflected in acounterclockwise direction along a substantially circular path, and theelectrons which travel to the right of the cable 6 are deflected in aclockwise direction along a substantially circular path, as shown inFig. 3. As a result, the electrons in the beam 7 are directed onto thecable 6 from substantially all aspects in the plane in which thecross-section of the beam 7 is extended, as shown in Fig. 3.

Referring more particularly to Fig. 3, the pole faces 11, 12, 13, 14must be so shaped as to give each portion of the electron beam 7 thedesired deflection. Maximum deflection is imparted to the outermostextremities of the electron beam 7, which bombard the cable 6 from theposterior aspect, while none is imparted to the central portion of theelectron beam 7, which bombards the cable 6 from the anterior aspect.Except for fringing effects, which are readily compensated for, andneglecting scatter, all electron paths will be circular and will havethe same radius of curvature in the magnetic fields, and all electronpaths will be rectilinear elsewhere. Fringing effects will occurprincipally in the vicinity of the gap between the pole faces 11 and 13and between the pole faces 12 and 14. The effect of scatter tends todiffuse the electron stream so as to augment uniformity of irradiation.

Having thus described the method of the invention, together withillustrative embodiments of apparatus for carrying out the method, it isto be understood that although specific terms are employed they are usedin a generic and descriptive sense and not for purposes of limitation,the scope of the invention being set forth in the following claims.Throughout the specification and claims hereof, the word plane is usedin a general sense and not in a precise sense, and includes planes whichare neither thin nor flat.

We claim:

1. Apparatus for irradiating an object with high-energy electronscomprising in combination an electron accelerator adapted to produce abeam of electrons whose cross-section is extended in at least one plane,means for supporting an object to be irradiated in the path of saidbeam, and means for producing two substantially parallel butsubstantially oppositely oriented magnetic fields in the path of saidbeam of extended cross section such that the electrons converge upon theobject from several aspects.

2. Apparatus for irradiating an object with high-energy electronscomprising in combination an electron accelerator adapted to produce abeam of electrons whose cross-section is extended in at least one plane,means for supporting an object to be irradiated in the path of saidbeam, and two pairs of opposed magnet pole faces flanking said object,the pole faces of each pair flanking said plane, the polarity of saidpole faces being such as to produce two substantially parallel butsubstantially oppositely oriented magnetic fields in the path of saidbeam of extended cross section, so that the electrons traveling betweenthe pole faces of each pair are deflected towards the object.

3. Apparatus for irradiating a continuous length of a product orproducts having a generally circular crosssection, comprising incombination an electron accelerator adapted to produce a beam ofelectrons whose cross-section is extended in at least one plane, meansfor drawing said continuous length through the path of said beam in adirection parallel to the longitudinal axis of the continuous length andat an angle to said plane and two pairs of opposed magnet pole facesflanking said continuous length, the pole faces of each pair flankingsaid plane, the polarity and shape of said pole faces being such as toproduce two substantially parallel but substantially oppositely orientedmagnetic fields in the path of said beam of extended cross section, sothat the electrons traveling between the pole faces of each pair aredeflected towards the object.

References Cited in the file of this patent UNITED STATES PATENTS2,741,704 Trump et a1 Apr. 10, 1956 2,785,313 Trump Mar. 12, 19572,824,969 Crowley-Milling Feb. 25, 1958

